1. Field of the Invention
The present invention relates to an optical information processing apparatus in which a light beam is irradiated onto an optical information recording medium such as an optical disk or the like and information is recorded and reproduced and/or erased.
2. Related Background Art
An optical information processing apparatus in which light from a light source is irradiated onto an optical recording medium and information is recorded and reproduced and/or erased has been recently studied and developed more and more from a viewpoint that an extremely large amount of information can be recorded.
As a recording medium which can record, reproduce, and erase information by a light beam, there has been known what is called a magneto-optic disk comprising a disk-shaped substrate made of glass, plastics, or the like and a perpendicular magnetization film which is formed on the substrate and ordinarily has a thickness of 100 to 500.ANG.. The perpendicular magnetization film is made of an amorphous alloy or the like and has a characteristic such that the film is magnetized in the direction perpendicular to the film surface.
To record information into a memory using such a magneto-optic disk, first, the magnetizing direction of the perpendicular magnetization film is previously aligned in one direction by effecting the magnetic field in the perpendicular direction on the magneto-optic disk. Then, the laser beam spot which has been digitally modulated by an information signal is irradiated onto the perpendicular magnetization film, thereby raising the temperature of the perpendicular magnetization film in this portion to the Curie point or higher. Thus, the magnetizing direction of the portion to which the laser beam spot was irradiated is reversed by the influence of the peripheral magnetic field and the logic value "1" (or "0") is recorded and a recording pit is formed. To raise the temperature of the perpendicular magnetization film to the Curie point or higher as mentioned above, a laser power of 8 to 10 mW is needed. Likewise, in the case of a low temperature, a large laser power of about 14 mW is also needed. When considering the efficiencies of various optical parts on the optical head, a laser power of about 30 to 35 mW is necessary as that of the semiconductor laser apparatus.
In such an optical information processing apparatus as mentioned above, when the life of the semiconductor laser as the light source has come, the laser needs to be exchanged. Particularly, in the magneto-optic disk memory, since light of a large power of about 14 mW is irradiated in the erasing mode, the life of the light source is short, and it is considered that the number of exchanging times of the light source is also large.
When the light source is exchanged, it is desirable to exchange the entire optical head, including the optical system, in order to make it unnecessary to perform positional adjustment with respect to other devices such as a photodetector and the like. The exchange of the optical head will be described with reference to FIG. 1. FIG. 1 shows only an electric circuit from a sensor to an actuator and the other portions are constructed as shown in an apparatus disclosed in, for instance, U.S. Pat. No. 4,293,944. Each of the focusing error signals and tracking error signal are obtained by what is called an astigmatism method and a push-pull method.
In FIG. 1, reference numeral 10 denotes a servo sensor which is divided into four sensor elements; reference numerals 22-1 to 22-4 indicate current/voltage converting amplifiers for converting four outputs of the servo sensor into voltages, respectively; 23-1 and 23-2 indicate adding amplifiers each for obtaining a signal indicative of the sum of the two output signals of each of the two sensor elements on a diagonal of the servo sensor 10; reference numeral 24 indicates a variable resistor to adjust the balance of outputs of the adding amplifiers 23-1 and 23-2; 25 a differential amplifier to obtain the difference between the outputs of the amplifiers 23-1 and 23-2 to thereby obtain a focusing error signal; 26 a variable resistor to adjust an amplitude of the focusing error signal to thereby standardize a voltage which is output in accordance with the focusing error; 27 a focusing error control circuit for outputting a signal to move an objective lens in accordance with the focusing error and for outputting a signal to initially execute the pull-in to a focal point; reference numerals 28-1 and 28-2 indicate amplifiers to drive a coil of a focusing actuator 29 to move &he objective lens in accordance with the output signal of the focusing error control circuit 27; 30-1 and 30-2 adding amplifiers for outputting signals indicative of the sums of the outputs of the left half two sensor elements and of the right half two sensor elements of the servo sensor 10; reference numeral 31 indicates a variable resistor to adjust the balance of outputs of the adding amplifiers 30-1 30-2; 32 a differential amplified to calculate the difference between the sum of the outputs of the left half sensor elements and of the right half sensor elements of the servo sensor 10 to thereby obtain a tracking error signal; 33 a variable resistor to standardize an output voltage in accordance with the tracking error; 34 a tracking control circuit for outputting a signal to move the objective lens in accordance with a tracking error and for outputting a signal to jump a laser beam spot to the adjacent track and the like; and 35-1 and reference numerals 35-2 indicate amplifiers to drive a coil of a tracking actuator 36 to move the objective lens in accordance with the output signal of the tracking control circuit 34.
The left half portion in FIG. 1 is assembled in the optical head and can be integrally exchanged. On the other hand, the right half portion in FIG. 1 is assembled in the electric circuit board on the main body side and this portion is not exchanged even when the optical head is exchanged.
Even in such an optical head constructed as a unit as mentioned above, there is a limitation of the accuracy of the mechanical positional adjustment among the elements assembled in the optical head. In addition, there is also a variation in the light emitting pattern of the semiconductor laser depending on the laser. Therefore, the outputs of the four sensor elements of the servo sensor 10 slightly differ for every optical head. Thus, in order to set an objective position of the focusing control to an in-focus position and to set an objective position of the tracking control to the center of the track, the offset needs to be adjusted by a circuit to arithmetically operate the sensor outputs. Such an offset adjustment is executed by the variable resistors 24 and 31, respectively. On the other hand, the adjustment to standardize the output of the difference signal and to equalize the gain of the control loop is executed by the variable resistors 26 and 33. The adjustments of the objective positions by the variable resistors 24 and 31 are performed while observing the waveform of the signal reproduced from a disk. The objective positions are adjusted to the positions such that the amplitude of the reproduced signal becomes maximum and the signal can be reproduced without a distortion.
However, since an apparatus such as an oscilloscope or the like is needed for the above adjustments, there is a problem that the user cannot perform the adjustments and the load of the maintenance on the manufacturer side is large.